Space station astronauts to replace failed equipment in spacewalk

WASHINGTON, May 22-- NASA astronauts on the International Space Station will conduct a contingency spacewalk on Tuesday to change out a data relay box that failed over the weekend, the U.S. space agency said.

Astronauts Peggy Whitson and Jack Fischer will venture out at around 8 a.m. EDT (1200 GMT) to replace the device, known as a multiplexer-demultiplexer (MDM) during a mission that is planned to last about two hours, NASA said.

The MDM is one of two fully redundant systems housed outside the orbiting laboratory that control radiators, solar arrays, cooling loops and other station hardware.

"The crew has never been in any danger, and the MDM failure, believed to be internal to the box itself, has had no impact on station activities," NASA said in a statement.

The other MDM is functioning perfectly, providing uninterrupted telemetry routing to the station's systems, it added.